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c#entity-frameworklinq-to-entitiesautomapper

Data projection in Entity Framework and Automapper

I want to use AutoMapper to construct a ViewModel (flattening - data projection) for use in an ASP.net MVC app.

var tmp = from x in db.Mailings select Mapper.Map<Mailing, MailingViewModel>(x);
return View(tmp.ToList());

Of course, when I try the sample above, I get the EF error "LINQ to Entities does not recognize the method ... method, and this method cannot be translated into a store expression."

I know it's possible to move the .ToList() before the Automapper does its magic, but then I fetch all the fields from the Db (and I only need 3 of 20 fields)

Is it possible to use that in a clean way. Clean = Not all the fields are fetched from the DB, but only the fields necessary for the ViewModel. Is it possible in Automapper? Or perhaps an other library? (without doing it manually ;) )

Solution

  • Yes this is very possible. See here http://www.devtrends.co.uk/blog/stop-using-automapper-in-your-data-access-code

    Edit: I've recently found that the basis to this already exists in AutoMapper. add a using statement for AutoMapper.QueryableExtensions and you are provided with an IQueryable extension called Project<>()